Lake Mead

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Running Dry? California Water Supply at Risk

View of Lake Mead on 9/9/10 (Original image courtesy of the Image Science & Analysis Laboratory, NASA Johnson Space Center. This version produced by Tom Yulsman of CEJournal)

Lake Mead is the largest reservoir in the country.  It’s located on the Colorado River, which provides water for about 27 million people in seven states, including millions of Californians.  In fact, California gets more than a trillion gallons of water from the Colorado River each year, directly from Lake Mead via the Colorado River Aqueduct which snakes across the desert.  Eighteen million people in Southern California are dependent on the Colorado for 40% of their water.  And for some agricultural operations, that percentage is more like 100.  Needless to say, it’s a critical source of water.

The thing is, after 11 years of dry conditions in the region, Lake Mead dropped to its lowest level ever in October.  And so far, it’s stayed there.  Since Hoover Dam was completed in the 1937 the water level has never been so low.  As of today, it’s at 38% of capacity.  And it’s not just Lake Mead that’s low.  The whole Colorado River storage system is at just 55% of capacity, so forget just filling it up with water from upstream.  Of course, winter’s on it’s way, and with that, precipitation, so the lake shouldn’t stay quite so low for long.  And, thanks to a wet year, Northern California’s reservoirs are doing well. Continue reading

When Will Lake Mead Go Dry?

Exposed turbine intakes and the "bathtub ring" at Lake Mead. Photo: Craig Miller

Exposed turbine intakes and the "bathtub ring" at Lake Mead. Photo: Craig Miller

You can see a slide show of the retreating waters at Lake Mead and Hoover Dam and listen to my radio feature from The California Report. Also, The American Experience will rerun its documentary on Hoover Dam, Monday night on most PBS stations.

The Las Vegas Sun has a digital clock on its website, counting down to a theoretical doomsday when the city’s principal source of water would go dry. Wagering on that question may not have found its way into the sports books on the Strip–but it did become a lively pastime among engineers and hydrologists, when a report emerged from San Diego’s Scripps Institution, with a dire forecast. The paper, by climate physicist Tim Barnett, put the odds at 50-50 that Lake Mead, the giant reservoir behind Hoover Dam, would reach “dead pool” by 2017. That’s the point at which the dam shuts down and neither hydroelectric power nor water emerges from it.

The Barnett study “definitely raised eyebrows throughout the basin,” admits Terry Fulp, deputy director of the U.S. Bureau of Reclamation’s Lower Colorado Region, which operates Hoover Dam and Lake Mead. As it turns out, Barnett was a bit pessimistic. Subsequent work by him and others revealed that he overestimated the evaporation rate at Lake Mead, and omitted inflows below a certain point on the river.

The bottom line, according to Balaji Rajagopalan at the University of Colorado: Doomsday is not quite that near at hand. But that doesn’t mean it’s not on the horizon. “After 2027, the demand increase outpaces the supply decrease,” Rajagopalan told me in a recent interview. “And that’s why much of the risk explodes from 2027 to 2057.”

All of these studies are couched in probabilities, much in the same way that the Corps of Engineers talks about a “100-year” flood. Rajagopalan says: “Even in our study, we have a 50% risk [of dead pool], but that occurs in 2057. And that makes a big difference in terms of water managers, what they can do.”

One of those managers is Pat Mulroy, who directs the Southern Nevada Water Authority. Her constituents rely on Lake Mead for 90% of their water, so she says she’s not inclined to wait around for a consensus. “I mean, during the entire period of the ‘90s when we were bickering with our friends in the lower basin over surpluses, there was zero probability that the drought that we’re currently in was going to happen,” Mulroy told me.  “I’ve lost confidence in probabilities.”

The Bureau’s Fulp says the Colorado system leans heavily on the huge water storage capacity of Lake Mead and its sister reservoir upstream, Lake Powell. “We’ve known for decades that this system is highly variable and that’s why so much storage was built.” When filled to capacity (which it was, more or less, 10 years ago), Lake Mead alone can hold enough to put an area the size of Pennsylvania under a foot of water. But a 10-year drought has left Mead at just over 40% of capacity (so think of flooding something more the size of Costa Rica). Just as current evidence and climate models both point toward lessening flows on the Colorado, many parts of the southwest still see relatively high population growth.

Scientists continue to run their statistical models aimed at handicapping the Colorado’s demise as a dependable bringer of water. But as Fulp sums it up, “It’s really a debate about when. It’s not really ‘if.”

I regret an error of my own that appeared in the radio feature. I misstated the number of people in southern Nevada who are dependent on water from the Colorado. The correct number is about two million.

Threats to Colorado River Water Supply

National Park Service

Photo: National Park Service

The Colorado River supplies water to approximately 27  million people in seven states and irrigates more than three million acres of farmland. In Southern California alone, it supplies 18 million Metropolitan Water District customers with 40 percent of their water.

So last year, when a study out of Scripps Institution of Oceanography reported that there’s a 50 percent chance that the Colorado River’s largest reservoir (and the largest reservoir in the United States), Lake Mead, will be dry by 2021, the news generated a lot of buzz.

But a new study out from the University of Colorado Boulder finds that despite a 10-year drought in the Colorado River system, the odds of draining the river’s delivery system before 2026 are pretty slim — below 10% in any given year.  Researchers say this is primarily due to the massive reservoir storage capacity along the Colorado — more than 60 million acre feet, which includes Lake Mead.  The reservoir system of the Colorado is currently at 59 percent of capacity, according to the study.

But the scientists predict that by mid-century, the Colorado could become less reliable unless water-management strategies change.

The researchers found that if climate change causes a 10 percent reduction in the Colorado River’s average stream flow as some recent studies predict ([PDF]), the chances of fully depleting the system’s reservoirs will exceed 25 percent by 2057.  If there is a 20 percent reduction in stream flow, the chances of deleption rise to 50 percent.

“On average, drying caused by climate change would increase the risk of fully depleting reservoir storage by nearly ten times more than the risk we expect from population pressures alone,” said lead study author Balaji Rajagopalan in a press release about the study.

The authors of the study conclude that the magnitude of the risk will depend not just on the amount of drying the region experiences, but also the types of water management and conservation strategies that are implemented in the near future.

For the last decade, California’s annual use of Colorado River water has varied from 4.5 to 5.2 million acre feet.

Photo by Adrian Fogg

Photo: Adrian Fogg